GPS technology has been widely applied in automobile navigation devices and personal navigation devices now. However, the error of GPS positioning signal may occur because the signals from satellite could be easily effected by shielding effects of terrain, buildings and weather conditions.
The industry solution has been provided by combining GPS technology with an inertia sensors (such as an accelerometer and a gyroscope). When the signal of the GPS device becomes weak or even failed due to the shielding effect (such as entering an underground parking lot), several approaches are provided for positioning, for example, an accelerometer and/or gyro. By continuously detecting acceleration by the accelerometer and/or detecting angular velocity by the gyro, the position of a car or person can be obtained, and the navigation function of the navigation device can work as normal in such a worse case. However, when the positions of the car or person are continuously obtained by the information from the accelerometer and/or the gyro, more and more calculation errors may be accumulated accordingly over time. That will cause the accuracy of the positions obtained by the navigation device being difficult to maintain.
A MEMS (Microelectromechanical systems) inertia sensing elements such as a magnetometer may be used to adjust the information from the gyro to avoid the accumulation of calculation errors over time. The location information measured by the magnetometer can be used to adjust the rotation angle calculated by the gyro, by which the accumulation of calculation errors can be reduced and the accuracy of the navigation device can be maintained and/or enhanced. In other word, the navigation device combining GPS device, accelerometer, gyro and magnetometer can prevent automobile navigation devices and personal navigation devices from the impact of the shielding effect.
With the innovation and applications of the MEMS (Microelectromechanical systems) inertia sensing elements on smart phones and navigation devices, the application scope of the navigation device can expand from an outdoor flat road to an indoor parking lot or to a large shopping mall. The MEMS magnetometer made with the MEMS technology has become a key element of the next-generation of automobile navigation devices and personal navigation devices.
A one-axis magnetometer is introduced herein in FIG. 1. In the uniaxial magnetometer 10, an electrical current I flows through a coil 14 on a twist plate 12. A magnetic field B will induce a Lorentz force F, and the Lorentz force F will drive the twist plate 12 to rotate. A sensing electrode (not shown) below the twist plate 12 can detect changes of the capacitance between the twist plate 12 and the sensing electrode. By the manner, the magnetic force of the position where the magnetometer 10 is located is obtained. If three uniaxial magnetometers 10 are disposed in three vertical axial directions, a three-axis magnetometer is formed. The location of the three-axis magnetometer can be deduced by calculating components of the geomagnetism on the three axial directions of the three-axis magnetometer, so as to realize a function similar to that of a compass.
At present a MEMS magnetometer usually adopts a single conductive coil design. Such MEMS magnetometers require large element size or require a large electrical current to sense the magnetic force, so it cannot satisfy the mobile phone product requirements of small size and low power consumption.
Another MEMS magnetometer adopts a design of a plurality of conductive coils. Referring to FIG. 2, the magnetometer 20 includes a plurality of coils 22 with a spiral path throughout a twist plate, but an extra cross-line structure 24 formed by a conductive layer 26 and an electrical insulation layer 28 are required to achieve electrical connections. In this way, the process requires more steps, and process cost and process risks are increased.
A MEMS micro-mirror is another application of the MEMS technology. Referring to FIG. 3, in the MEMS micro-mirror 30, the Lorentz force is produced after that the electrical current flowing through a coil 32 on a twist plate interacts with a permanent magnet 38. The Lorentz is used to drive the twist plate to rotate and to drive a mirror 34 on the twist plate to rotate accordingly. However, the coil 32 still requires the cross-line structure 36 to achieve electrical connection. Similarly, the process requires more steps, and process cost and process risks are increased.